Directional couplers



March 29, 1960 G. E. KORB DIRECTIONAL COUPLERS Filed Nov. 4, 1957 FIG.

INVENTOR G E. KORE ATTORNEY ture but stronger alloys.

attached thereto.

United States Patent DIRECTIONAL COUPLERS Application November '4, 1957,Serial No."694,247

4 Claims. (Cl. 333-) This invention relates to electrical wave couplingdevices and more particularly to an improved method of fabricatingcross-guide directional couplers.

In both experimental work and in small production runs, there has been aneed for an improved method of fabricating cross-guide directionalcouplers. Presently employed production methods which are bothstructurally and electrically sound employ casting or electroformingtechniques. be made, however, the use of these methods of production isparticularly uneconomical. Furthermore, the units so manufactured lackthe flexibility required of this type of transmission component inexperimental development where changes in the method and amount or.coupling between guides are often made in the course of the work.

When only a small number of couplers are to be made, the most popularmethod of fabrication presentlyemployed utilizes the so called commonwall coupling plate. plate, as thick as the waveguide wall and the samewidth as the waveguide to be used,'is soldered into an opening cut tothe plate size and thickness between the two waveguides to be coupled.Generally the guides are coupled at right angles to each other. Theplate thus forms a common wall over the common region or junction of thecrossed guides. The size of the coupling holes and their reltaivepositions can be controlled to closer tolerances before soldering to agreater extent in this manner of construction than by attempting to putthe coupling holes in one guide and removing the wall from only themating crossed guide. With either method of construction however, theassembly is soft soldered together to avoid the heat distortion causedby the higher tempera- The result is a component of low mechanicalstrength which is unable to resist the stress and strain imposed byother microwave components In addition, unless extreme care is used whensoldering, poor joints result which impair the electrical performance ofthe coupler.

It is therefore an object of this invention to provide an economicalmethod of constructing cross-guide couplers for the transfer ofelectromagnetic wave energy which are both mechanically strongandelectrically efficient.

Couplers built in accordance with the techniques outlined above arefundamentally permanent structures. As

In this method of construction a precision square When only a smallnumber of units' are to such they do not lend themselves to experimentalwork where it is often very desirable to change the mode of coupling orthe amount of coupling between the'two In accordance with the presentinvention a common 1 wall plate and waveguides of dovetailedconstruction are invention;

2,930,995 Patented Mar. 29, 1960 provided. In this dovetailedcouplenzthe edges or the coupling plate are tapered at some angle incontrastto the straight edges previously used. Similarly, the edgestransverse to the guide axes along the'aperturescut in the guide wallsto form the coupling region are also tapered to receive the taperedcommon wall plate. The plate is slid transversely into place in thefirst guide there by replacing the portion previously removed therefrom.The coupling plate is made slightly larger than the first waveguidewidth to allow for the overlap caused by the dovetailed edges whichengage the second waveguide. The latter is similarly slid into place bymovement transverse to its axis. J

It is a feature of' the present invention thata' coupler so constructedmay be assembled without soldering and when so assembled with be bothmechanically strong and electrically efiicient. It is a further, featurethat numerous common wall plates may be made with an assortment ofcoupling apertures of different design and size which ma y be easily andquickly replaced in the" coupler.

' Where a more permanent structure is desired, the edge angles. on thecommon wall plate are made slightly smaller than the corresponding edgeangles on the guide walls. In such a case, a small fillet is formed whenthe plate is in place into which solder may be flowed. It will be noted,however, that the solder is not relied upon for mechanical strength norfor electrical eificiency,'the latter being determined to a great extentby the knife, edges on the plate which make intimate contact along thelength of the junctions of the guide walls and the common wall plate.

These and other objects and features, the nature of the presentinvention and its various advantages, will appear more fully uponconsideration of the specific illustrative embodiments shown in theaccompanying drawings and described in the following detaileddescription of these drawings. 7 v, v

'In the drawings: I i

Fig. 1 is a perspective view of a partially assembled cross-guidecoupler made in accordance with-the present Fig. 2 is a perspective viewof a partially assembled cross-guide coupler showing the solder filletformed by the dissimilar dovetail angles.

Referring now to the drawings and in particular to Fig. 1, there isshown a partially assembled cross-guide coupler constructed inaccordance with the invention comprising 'a pair of conductively boundedrectangular transmission lines 10 and 11 for guiding electromagneticwave energy and the common wall" coupling plate 14; Transmission lines10 and 11 have a wide internal cross-sectional dimension of at leastone-half wavelength of the wave energy to be conducted therein, andanarrow dimension substantially one-half of the'wide dimension. A portionof wide walls 8' and 9 of guides 10 and ll'have been cut away leavingapertures 12 and 13, respectively, in the guides. Extending transverselyacross the width ofv guide 10 are the edgesand 16 in wall 8 beveled atan angle to the plane of wall such that the longitudinal distance alongthe inside of wall Sbetween edges 15 and .16" is greater than thelongitudinal distance alongthe outside of wall 8 between edges 15' and16'. Similarly, edges 17' and 18' extending transversely acrossguide113th wall 9 are beveled in a like manner at an angle'to the plane ofwall 9. v 1

v Partially inserted over aperture 12 is the common wall coupling plate14. The latter comprises a conductive guides 10 and 11. Aperture 23 isdesigned in accordance w1th procedures well known in the art asillustrated, for

example, in United States Patent 2,473,274, issued to eouplerasillustrated in Fig. 2 may be used,

asse s-e W. E. Bradley on June\14, "1949. As disclosed therein, aperture23 may comprise a pa'ii'ormuttranyperpendie: ular slits so disposed thatunidirectional traveling waves the first guide produceunidirectional-trawling waves inthefsecondguide. "f' a f i Thetransversely extending edges 15 and 16 of plate. 14 are beveled atlthesame angle as edges 15" and 16, of guide 10. Plate 14 may thenbe'slidably inserted'betweeli edges 15 and 16' to cover aperture 1221sindicated by arrow 20. The dimensions of plate 14 and aperture 12 aresuch that the plate is tightly held in intimate contact with the guide,and forms a smoothly continuous surface along the inside thereof. Inaddition to forming a good electrical connection for the passage ofelectromagnetic wave energy within the guide, a strong mechanical bondisachieved between the plate'and the guide.

When plate '14 is in Position covering aperture 12, edgesf17 and'lfiextend slightly over the sides of guide 11 sufliciently to'engage edges17"and 18. of guide 11.

The latter is connected by aligning edges 17 and '11 and 18and 18,? andsliding guide 11 over plate lens indiefated by arrow21.

When fully engaged, guide 11 is held in intimate contact with plate14'formi'ng a'continu'ous conductive Stifface within the guide for thepropagation or electromagnetic wave energy therethrough. In addition, astrong mechanical bond is established between guide 11 and plate 14. i

' Coupling plate 14, thus. provides both the mechanical and electricallink between the two coupled guides. By virtue of the dovetailedconstruction a strong solder-less mechanical bond is established. Inaddition, plate 14 forms an electrically continuous common wall betweenthe guides in which there is located the desired coupling means in theform of apertures or otherwise.

Also illustrated in Fig. 1 is a second common wall plate 22. The latteris merely illustrative of the many plates which may readily be insertedin place of plate 14 merely by sliding guide 11 off and sliding plate 14out.

This'operation maybe performed in a matter of seconds thus making thistype of dovetailed coupler extremely handy in laboratory work wherefrequent changes in coupling may be desired. a i

Where a more permanent structure is required, the

In this embodiment of the invention, edges 32 and 33 of guide 39 arebeveled at a slightly diflerent angle than edges 34 and 35. of plate 31.Thus, when fully engaged, fillets 36 and 37 are formed between theedges. The space thus left may then be, filled with solder to forma'continuous surface. It should be noticed, however, that the solder isnot relied upon either for electrical continuity or mechanical strength.When in place, the knife edges 4% and 41 of plate 31 come in closecontact with the inside of the waveguide to provide the necessaryelectrical path for wave energy being propagated within the guide.Similarly, by undercutting the edges 32 and 33, the plate is firmly heldin place with or without the application of solder along the fillets.Thus, soft solders may be used thereby avoiding the danger of warping ofthe guide due to high temperatures. which would be required if thestronger alloy solders had to be used to provide the necessarymechanical strength.

' Edges 38 and 39 may be cut either to engage, the second waveguide (notshown) or they may be cut at a slightly different angle to form a secondset of fillets when the cross-guide is in position, a

In all cases it is understood that the above-described arrangements" are'sir'fiply'illust'rat'ive 'o f s'anair'niniser of the many possiblespecific embodiments which can represent applications of the principlesof the invention. Numerous and varied other arrangements can readily bedevised in accordance with these principles by those skilled in the artwithout departing from the spirit an scope of the invention.

What is claimed is':

1 An electromagnetic wave energy transfer system comprising a pair ofrectangular waveguides each having a portion of a wall removed to forman aperture therein,

the guide vwall edges defining said apertures and oblique V to the axisof said respective guides being beveled at an angle to said walls, andmeans for physically connecting said guides including a conductive platehaving beveled edges dimensioned to be slidably received by saidapertures and coupling means disposed along said plate for coupling'said' wave energy between said pair of'wave guides." 2. Means'forelectrically and mechanically intercon necting apair of conductivelybounded rectangular waveguides" comprising a first waveguide' having aportion of a wall removed to form a commonwall region, the wall edgesalong said region oblique to the axis of said first guide being beveledat an angle such that the longitudinal distance between edges along theinside. of said 'first guide is greater than the longitudinal distancebetween edges along the outside of said first guide, a conductive memberproportioned to have the same size and shape as said common wall regionhaving a first pair and a second pair of opposite edges beveled to beslidably received by said first guide in said common wall region forminga tightly fitting contact between said first guide and said member alongsaid first pair of opposite edges, a second waveguide having a portionof a'wall removed to form a common wall region, the wall edges alongsaid region oblique to the axis of said second guide being beveled at anangle such that the longitudinal distari'ce between edges along theinside of said second guide is greater than the longitudinal distancebetween edges along the outside of said second guide, said common wallregion in said second guide proportioned to be slidably received by saidmember along said second pair of opposite edges forming a tight fittingcontact along said second pair of edges, and coupling means in saidmember to electrically couple said first guideto'said second guide.

3. The combination according to claim 2 wherein the bevel angle on saidmember is the same as the bevel angle on said guide walls. a

4. The combination according to claim 2 wherein the bevel angle on saidmember is difierent than the bevel angle on said guide walls formingfillets along said-edges when said member is slidably received by saidguide, said fillets being filled with solder to bond said member to'said guides.

References Cited in the file of this patent UNITED STATES PATENTSSwitzerland Mar. 16,

